The present invention relates to a filter in the inlet stream of a heating or air-conditioning system of a motor vehicle for retaining noxious gaseous components of the air. The filter has a tubular form which has air flowing through it transversely to its central longitudinal axis and one casing end which can be optionally closed or opened by a flap.
A filter is shown in DE-OS 36 26 391 which provides an advantage that, in an atmosphere which is free from or low in noxious substances, the filter can be deactivated by opening a flap and, at the same time, an increased throughflow of air is achieved. In the filter mode, the filter's absorption capacity is exhausted after a specific time so that the filter has to be replaced. This period of time can be lengthened by desorbing the filter at specific time intervals. It is also possible to shorten this process substantially by heating the filter material.
It is an object of the present invention to provide a desorption process which can be carried out quickly, in which case the expenditure necessary for this should be as low as possible.
This object is achieved in accordance with the present invention by constructing a filter comprising layered discs filled with activated carbon and separated from one another in each case by an intermediate layer consisting of material with good heat-conducting properties. The discs and the intermediate layers can be clamped to each other by armatures penetrating the discs in the direction of the central longitudinal axis of the tubular section. The armatures, which have a direct heat-conducting connection to the intermediate layers, can be heated.
In order to heat up the armatures, they are configured as a tube and have cooling water flowing therethrough, if necessary. However, each tube can also have a heating unit connected to an electrical voltage source. The heating can be switched on as desired or even automatically, in which case, when switching on, a timing switch which switches off the heating process again after a predetermined time has expired is expediently started up. During the desorption phase, the air leaving the filter is fed directly into the open air, preferably avoiding the passenger compartment of the motor vehicle. This is achieved in a particularly simple manner by a reversal of the direction of rotation of a heater blower such that air is passed through the filter in the opposite direction to that used in the filter mode.